1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a miniaturized display device having a touch panel which is used in a mobile phone or the like.
2. Description of the Related Art
A liquid crystal display device includes a TFT substrate on which pixel electrodes, thin film transistors (TFT) and the like are formed in a matrix array, a color filter substrate which faces the TFT substrate in an opposed manner and forms color filters and the like thereon at positions corresponding to the pixel electrodes formed on the TFT substrate, and liquid crystal which is sandwiched between the TFT substrate and the color filter substrate. An image is formed by controlling optical transmissivity of liquid crystal molecules for every pixel.
The liquid crystal display device can be formed into a miniaturized and thin shape and hence, the liquid crystal display device is used in various usages including a mobile phone and the like. Recently, various kinds of applications are added to a mobile phone. Further, an input device of the mobile phone is also requested to possess a function which allows a user to perform inputting with his finger using a touch panel in addition to a conventional key-button operation. In such a case, the touch panel is mounted on a color-filter-substrate side of a liquid crystal display panel.
On the other hand, the liquid crystal display device is strongly requested to satisfy a demand for the reduction of an external shape size of a set while maintaining a screen at a fixed size and a demand for the reduction of thickness of a liquid crystal display panel simultaneously. To reduce a thickness of the liquid crystal display panel, after manufacturing the liquid crystal display panel, an outer side of the liquid crystal display panel is polished so as to reduce a thickness of the liquid crystal display panel. With respect to a TFT substrate which constitutes the liquid crystal display panel and forms pixel electrodes and TFTs (thin film transistors) and the like thereon and a color filter substrate which also constitutes the liquid crystal display panel and forms color filters thereon, a glass substrate for forming the TFT substrate or the color filter substrate is standardized to have a thickness of 0.5 mm or 0.7 mm, for example. It is difficult to obtain such standardized glass substrates at the market. Further, an extremely thin glass substrate has drawbacks in manufacturing steps with respect to mechanical strength, deflection or the like thus lowering a manufacturing yield ratio. As a result, a liquid crystal display panel is formed using a standardized glass substrate and, thereafter, an outer surface of the liquid crystal display panel is polished so as to reduce a thickness of the liquid crystal display panel.
When the liquid crystal display panel becomes thin, the liquid crystal display panel suffers from mechanical strength. That is, when mechanical pressure is applied to a display screen of the liquid crystal display panel, there exists a possibility that the liquid crystal display panel is broken. On the other hand, a thickness of the touch panel is small and hence, when the touch panel is installed in the liquid crystal display panel, the same problem also arises.
To prevent the liquid crystal display panel from being broken by an external force, a front window made of a resin or glass is mounted on a screen side of the liquid crystal display panel. In this case, an air layer is present between the liquid crystal display panel and the touch panel or between the touch panel and the front window, and transmissivity of light from a backlight is reduced due to the reflection of light from an interface at such a portion.
To overcome this drawback, JP-A-2008-83491 (patent document 1) discloses the constitution where an adhesive layer or a reflection preventing film is formed between the liquid crystal display panel and the touch panel or between the touch panel and the front window.